Osteochondral implant fixation procedure and bone dilator used in same

ABSTRACT

A surgical procedure for implanting a graft according to which a dilator is inserted in a recipient opening and the graft is inserted in the dilator to cause outward expansion of the dilator into engagement with the portion of a bone surrounding the opening. After the dilator is removed from the opening, the bone surrounding the opening collapses around the graft to secure the graft in the opening.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 11/340,024, filed Jan. 25, 2006, now U.S. Pat. No. ______, the entirety of which is incorporated by reference.

BACKGROUND

This invention relates to an improved osteochondral implant fixation method and, more particularly, to such a method in which a recipient hole is prepared for receiving a graft.

In the human body, the knee consists of three bones—a femur, a tibia, and a patella—that are held in place by various ligaments. The corresponding chondral areas of the femur and the tibia form a hinge joint, and the patella protects the joint. Portions of the latter areas, as well as the underside of the patella, are covered with an articular cartilage which allow the femur and the tibia to smoothly glide against each other without causing damage.

The articular cartilage often tears, usually due to traumatic injury (often seen in athletics) and degenerative processes (seen in older patients). This tearing does not heal well due to the lack of nerves, blood vessels and lymphatic systems; and the resultant knee pain, swelling and limited motion of the bone(s) must be addressed.

Damaged adult cartilages have historically been treated by a variety of surgical interventions including lavage, arthroscopic debridement, and repair stimulation, all of which provide less than optimum results.

Another known treatment involves removal and replacement of the damaged cartilage with a prosthetic device. However, the known artificial prostheses have largely been unsuccessful since they are deficient in the elastic, and therefore in the shock-absorbing, properties characteristic of the cartilage. Moreover, the known artificial devices have not proven able to withstand the forces inherent to routine knee joint function.

In an attempt to overcome the problems associated with the above techniques, osteochondral transplantation, also known as “mosaicplasty” and “OATS”, has been used to repair articular cartilages. This procedure involves removing injured tissue from the articular opening and drilling cylindrical holes in the base of the opening and underlying bone. Cylindrical plugs, consisting of healthy cartilage overlying bone, are obtained from another area of the patient, typically from a lower weight-bearing region of the joint under repair, or from a donor patient, and are implanted in the holes. However, in these cases, if the hole is too large, the graft can rotate in the hole and become loose, which will prevent integration with the surrounding tissues. If the hole is too small, significant cellular damage can occur to the graft during the implantation.

An embodiment of the present invention involves a graft implantation technique that overcomes the above problems.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a elevational view of a human knee with certain parts removed in the interest of clarity.

FIG. 2 is an exploded view, illustrating the grafting technique according to an embodiment of the invention.

FIGS. 3 and 4 are enlarged sectional views depicting steps in the grafting technique.

DETAILED DESCRIPTION

Referring to FIG. 1 of the drawing, the reference numeral 10 refers, in general, to a knee area of a human including a femur 12 and a tibia 14 whose respective chondral areas are in close proximity to form a joint. A cartilage 16 extends over a portion of the chondral area of the femur 12, and a meniscus 18 overlies a portion of the chondral area of the tibia 14 and extends between the tibia and the cartilage. The patella, as well as the related tendons and quadriceps that also form part of the knee, are not shown in the interest of clarity.

It will be assumed that a portion of the cartilage 16 in the chrondral area of the femur 12 has been damaged and removed by the surgeon, or has worn away, exposing a damaged area, or defect 12 a, and that it is desired to implant a graft in the defect.

Referring to FIG. 2, a graft 20 is obtained from one of several sources. For example, it could be harvested from another area of the patient/recipient, such as a undamaged non-load bearing area of the femur or tibia that has cartilage extending over a portion of its chondral area. Alternately it could be obtained from a cadaveric donor, a living donor, or it could be of xenogenic origin, or of an artificial substitute material.

The graft 20 has a circular cross-section and includes a bony portion 22 and a cartilage portion 24 overlying the bony portion 22.

A recipient opening 12 b is formed in the defect 12 a that is shaped the same as the graft 20, but has a diameter that is slightly smaller than that of the graft. An exemplary technique for forming the opening 12 b would be to drill a hole in the femur 12 to a depth substantially corresponding to the height of the graft 20.

A dilator 30 is provided that consists of a hollow body member 32 having a wall that tapers radially inwardly from one end 32 a of the body member to its other end 32 b to form a hollow frusto-cone. An annular lip 32 c extends outwardly from the end 32 a, and a series of spaced, longitudinal slits, or slots, 32 d are formed through the wall forming the body member 32 to add flexibility to the wall, for reasons to be described.

The diameter of the end 32 b of the body member 32 is less than the diameter of the opening 12 b so that the end can be inserted in the opening. The diameter of the end 32 a is greater than that of the opening 12 b to cause expansion of the opening in a manner to be described. The diameter of the end 32 a of the body member 32 is greater than the diameter of the graft 20 so as to receive the graft, and the diameter of the end 32 b is less than that of the graft so that, when the graft is inserted in the body member, the body member will expand, also in a manner to be described.

Referring to FIGS. 2 and 3, after the opening 12 b is formed during the surgical procedure, the end 32 b of the dilator 30 is initially inserted into the opening 12 b either by hand or using any suitable instrument. Then, as the dilator 30 is pushed, or forced, in an axial direction into the opening 12 b, its tapered outer surface engages the inner wall of the opening and exerts outwardly-directed radial forces against the latter wall. Sufficient force is exerted to drive the dilator 30 axially into the opening until the end 32 b engages the bottom of the opening 12 b and the lip 32 c engages the chrondral surface of the femur 12 surrounding the opening 12 b. Due to the fact that the diameter of the end 32 a, as well as a portion of the tapered body member 32 adjacent the latter end (the lower portion of the dilator 32 as viewed in FIG. 2), is greater than that of the opening 12 b, the opening, and, more particularly, the tissue and bony portion of the femur 12 defining the opening, is expanded radially outwardly as the dilator moves to its completely embedded position in the opening shown in FIG. 3.

The graft 20 is then inserted into the opening 12 b either by hand or using any suitable instrument. The graft 20 is then pushed, or forced, in an axial direction into the body member 32 with the outer surface of the graft engaging the inner surface of the tapered inner wall of the body member 32, to exert outwardly-directed radial forces against the latter wall. Due to the fact that the diameter of the graft 20 is greater than the upper portion of the tapered body member 32 as viewed in FIGS. 2 and 3, the body member is expanded radially outwardly, aided by the slots 32 d, as the graft moves axially in the body member. This expansion of the body member 32 causes corresponding additional expansion of the opening 12 b. This movement continues until the leading end of the graft 20 engages the bottom of the opening 12 b, as shown in FIG. 3. In the position of FIG. 3, the dilator 30 extends in the opening 12 b in a snug fit and the graft 20 extends in the dilator in a snug fit.

With reference to FIG. 4, the dilator 30 is manually extracted from the opening in the direction shown by the arrow, thus forming an interface between the graft 20 and the wall of the femur 12 defining the opening 12 b. The expanded bony portion and tissue of the femur 12 surrounding the graft 20 will then collapse around the graft, thus producing compression that retains the graft in the opening 12 b. This prevents any relative movement between the graft 20 and the opening 12 b and promotes integration of the graft with the surrounding bone and tissue of the femur 12.

Variations

1. The dimensions of the graft, the dilator and/or the opening, can vary within the scope of the invention.

2. The relative dimensions between the graft, the dilator and/or the opening, can vary within the scope of the invention.

3. The shape of the graft, the dilator, and or the opening can vary within the scope of the invention. For example, the cross-section of the graft, the dilator, and the opening can be of a polyagonal shape as disclosed in copending U.S. patent application Ser. No. 11/120,136, filed Apr. 30, 2005, the disclosure of which is hereby incorporated by reference.

4. The procedure and dilator discussed above are equally applicable to any animal species in addition to humans.

5. The graft can be harvested from the patient or another human, or can be a xenogenic source, or can be a substitute material.

6. The spatial references mentioned above, such as “upper”, “lower”, “under”, “over”, “between”, “outer”, “inner” and “surrounding” are for the purpose of illustration only and do not limit the specific orientation or location of the components described above.

Those skilled in the art will readily appreciate that many other variations and modifications of the embodiments described above can be made without materially departing from the novel teachings and advantages of this invention. Accordingly, all such variations and modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. 

1. A dilator for use in implanting a graft in an opening in an animal, the dilator comprising: a dilator having a hollow frusto conical configuration having a distal and proximal end; said dilator having a continuous tapered outer surface extending from said distal end to said proximal end of said dilator; said continuous tapered outer surface configured to engage a bone in order to radially expand the bone outwardly as the dilator is advanced into an opening; one end of the body member having a cross-section less than the cross-section of the opening for insertion into the opening; and the other end of the body member having a cross-section greater than the cross-section of the opening so that insertion of the body member in the opening expands the opening.
 2. The dilator of claim 1, wherein the cross-section of the other end of the body member is greater than the cross-section of a graft so as to receive the graft.
 3. The dilator of claim 1, wherein the cross-section of the one end of the body member is less than that of a graft so that the insertion of the graft expands the body member radially outwardly to further expand the opening.
 4. The dilator of claim 3, further comprising slots in the wall of the body member to promote the expansion.
 5. The dilator of claim 3, wherein the opening, the dilator, and the graft all have a circular cross-section and wherein the expansion is in the radial direction.
 6. The dilator of claim 1, wherein the other end of the body member has a cross-section greater than the cross-section of the opening so that insertion of the body member in the opening expands the opening.
 7. The dilator of claim 1, wherein the cross-section of the other end of the body member is greater than the cross-section of the graft so as to receive the graft.
 8. The dilator of claim 1, further comprising slots in the wall of the body member to promote the expansion.
 9. The dilator of claim 8, wherein the opening, the dilator, and the graft all have a circular cross-section and wherein the expansion is in the radial direction. 